<div class="test-center"></div>
<style>
.test-center{
    background: rgb(180, 216, 113);
    border: 1px solid #ccc;
    height: 500px;
    width: 200px;
    position: fixed;
    top: 0;
    bottom: 0;
    left: 0;
    right: 0;
    margin: auto;
}
</style>